Fuel injection valve for internal combustion engines

ABSTRACT

A fuel injection valve for internal combustion engines, having a housing ( 1 ) in which a pistonlike outer valve needle ( 10 ) is disposed longitudinally displaceably in a bore ( 3 ) and cooperates with a valve seat ( 13 ), embodied on the end of the bore ( 3 ) toward the combustion chamber, to control at least one injection opening ( 7 ). A control chamber ( 24 ) is embodied in the housing ( 1 ), the pressure in the control chamber ( 24 ) being regulatable by a valve ( 33 ), and by the pressure in the control chamber ( 24 ) a closing force is exerted at least indirectly on the outer valve needle ( 10 ) in the direction of the valve seat ( 13 ). At least one pressure face ( 9; 101 ) is embodied on the outer valve needle ( 10 ) and is acted upon by the pressure in a pressure chamber ( 5 ), which is embodied between the outer valve needle ( 10 ) and the wall of the bore ( 3 ) and extends as far as the valve seat ( 13 ), so that an opening force on the outer valve needle ( 10 ) results that is oriented counter to the closing force. An inner valve needle ( 12 ) is guided in the outer valve needle ( 10 ) and controls at least one additional injection opening ( 7 ) on the valve seat ( 13 ) and is acted upon by the pressure in the control chamber ( 24 ) at least indirectly in the direction of the valve seat ( 13 ) (FIG.  1 ).

PRIOR ART

To reduce emissions and increase the efficiency of internal combustionengines with direct fuel injection, one goal is to inject the fuel intothe combustion chamber of the engine in as finely-atomized a form aspossible. To that end, first the injection pressure at which the fuel isinjected through the fuel injection valve is increased. Second, thenumber of injection ports of the fuel injection valve is increased, sothat the diameter of the individual injection ports can be reduced. Thegoal of this provision is to increase the energy of injection streamswhile at the same time reducing the droplet diameter. If very smallquantities are to be fed, then when the pressures at the fuel injectionvalve are high the injection times are quite short. The course ofcombustion is consequently powerful and correspondingly noisy.

From European Patent Application EP 0 470 348 A1, for instance, a fuelinjection valve of variable injection cross section is known, in whichtwo rows of injection openings are embodied. These injection openingsare controlled by an inner valve needle and a tube surrounding the valveneedle; both the tube and the inner needle are acted on by closingsprings, which press them into contact with a valve seat, as a result ofwhich the injection openings are closed. If fuel at high pressure isintroduced into corresponding pressure chambers, then the tube and theinner needle are acted upon by the fuel pressure in these pressurechambers. Depending on the pressure of the fuel introduced, either onlythe inner needle lifts from the valve seat and uncovers the first row ofinjection openings, or the inner needle and tube lift up from the valveseat successively, so that both rows of injection openings are opened insuccession. The opening of the inner needle and the tube is accordinglypressure-controlled, so that the successive opening of the inner needleand the outer tube is achieved by means of a skillful design of thepressure faces and of the force of the closing springs.

Stroke-controlled fuel injection systems are also known from the priorart, in which a valve needle has a pressure face that is constantlyurged in the opening direction by fuel at high pressure. The contraryforce is generated not by a closing spring but rather hydraulically by avalve piston, which acts on the valve needle and in turn, because of thefuel pressure in a control chamber, exerts a closing force on the valveneedle. As an example here, German Patent Disclosure DE 198 27 267 A1can be named. By varying the fuel pressure in the control chamber, theclosing force on the valve needle is changed, so that this needle ismoved against the pressure face by the hydraulic force. Suchstroke-controlled fuel injection systems are used in many moderninternal combustion engines, especially for self-igniting engines inpassenger cars.

A combination of the two systems, that is, of the variable injectioncross section and the stroke-controlled injection system, would beespecially advantageous to further optimize the combustion process.Until now, however, it was not possible without major effort to adoptthe variable injection cross section to the stroke-controlled systemswithout making further modifications. Doing so requires complicatedsealing edges or additional control valves, which are complicated tomanufacture and expensive.

ADVANTAGES OF THE INVENTION

The fuel injection valve of the invention having the definitivecharacteristics of claim 1 has the advantage over the prior art thatwith a stroke-controlled injection system, two rows of injectionopenings can be opened successively, and a shaping of the course ofinjection is thus possible without requiring additional control edges orcontrol valves. An inner valve needle is guided in the outer valveneedle, and both the outer valve needle and the inner valve needlecontrol at least one injection opening. In the fuel injection valve, afuel-filled control chamber is embodied, by whose pressure the valveneedles are urged at least indirectly in the direction of the valveseat. If the pressure in the control chamber changes, then the closingforce exerted by the valve needles also changes, so that triggering ofthe injection openings is possible.

In an advantageous feature of the invention, a throttle connection isformed by the opening stroke motion of the outer valve needle, so thatthe inner valve needle is no longer acted upon by the pressure in thecontrol chamber. As a result, the closing force on the inner valveneedle is reduced in a simple way, without requiring a control edge oran additional valve.

In an advantageous feature, the outer valve needle is connected to anouter piston rod, whose end face is acted upon by the pressure in thecontrol chamber and thereby generates the closing force on the valvemember. As a result, the function of the valve needle and of thepressure-actuated piston rod can advantageously be separated from oneanother and thus each designed optimally.

In a further advantageous feature, the throttle connection is formedbetween the face end of the piston rod and a stationary bottom face, sothat the throttle connection can be embodied in a simple way that isaccordingly easy to manufacture.

In another advantageous feature, the inner valve needle is alsoconnected to an inner piston rod, whose face end is likewise acted uponby the pressure in the pressure chamber and thus generates the closingforce on the inner valve needle. By this means as well, the function ofthe valve needle and of the piston rod can be separated.

In still another advantageous feature, the inner piston rod is guided inthe outer piston rod, so that both piston rods are coaxial to oneanother. As a result, the connection of the outer piston rod to theouter valve needle, and of the inner valve needle to the inner pistonrod, can advantageously be achieved in a simple way.

In a further advantageous feature, the inner piston rod, in the openingstroke motion of the inner valve needle, comes to rest on a stop faceembodied on the inside of the outer piston rod. As a result, the strokestop of the inner valve needle is realized in a simple way, withouthaving to embody a stroke stop on the housing of the fuel injectionvalve.

In still another advantageous feature, the outer piston rod, on its endremote from the combustion chamber, has an inward-projecting region. Asa result, an inner control chamber is defined by the outer valve needle,the inward-projecting region, and the inner valve needle, and this innercontrol chamber communicates with the control chamber, the communicationbeing embodied in the form of a connecting bore. As a result, thepressure equalization between the control chamber and the inner controlchamber and thus the closing force on the inner valve needle in theopening stroke motion can be adapted by means of the design of the valveneedle, so that a defined, successive opening of the outer valve needleand the inner valve needle takes place, and thus the desired shaping ofthe injection course takes place as well.

In still another advantageous feature of the invention, the inner valveneedle has a pressure face, which is not acted upon by the pressure inthe pressure chamber until after the outer valve needle has lifted fromthe valve seat. As a result, an opening force on the inner valve needleis produced only when an injection is to occur. Because of this, noopening force acts on the inner valve needle between injections, andthis needle always securely closes the injection openings assigned toit.

In still another advantageous feature of the invention, the pressure inthe control chamber is established by a communication, controllable by avalve, with a leak fuel chamber. Thus for controlling the pressure, onlythis one 2/2-port directional control valve is required, since the innerthrottle remains unchanged.

In another advantageous feature of the invention, the outer piston rod,in the opening stroke motion of the outer valve needle, closes the innerthrottle at least partly. The result is a further drop in the pressurein the control chamber, so that the closing force on the inner valveneedle decreases further. By means of a suitable design of the openingforces on the valve needles, it can be attained that the inner valveneedle executes an opening stroke motion only after the outer valveneedle has closed the inner throttle, and thus the injection openingsare opened successively. In this way, the injection rate at the onset ofthe injection is less than during the main injection, in which all theinjection openings are uncovered, so that a shaping of the injectioncourse is achieved.

Further advantages and advantageous features of the subject of theinvention can be learned from the description of the drawings and fromthe claims.

DRAWINGS

In the drawings, one exemplary embodiment of the fuel injection valve ofthe invention is shown.

FIG. 1 shows a longitudinal section through a fuel injection valve ofthe invention;

FIG. 2 shows an enlargement of FIG. 1 in the region marked II;

FIG. 3 shows an enlargement of FIG. 1 in the region marked III;

FIG. 4 shows the same detail as FIG. 3, but the outer piston rod is in adifferent switching position.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In FIG. 1, one exemplary embodiment of the fuel injection valve of theinvention is shown in longitudinal section. The fuel injection valveincludes a housing 1, which can be constructed in multiple parts. On itsend region toward the combustion chamber, the housing 1 has a bore 3, inwhich a pistonlike outer valve needle 10 is disposed. The outer valveneedle 10 is guided sealingly in the bore 3 in a portion remote from thecombustion chamber and tapers toward the combustion chamber, forming apressure shoulder 9. On the end toward the combustion chamber, the outervalve needle 10 changes into a conical pressure face 101 and finallyinto a likewise conical valve sealing face 11; the pressure face 11, inthe closing position of the outer valve needle 10, comes to rest on avalve seat 13 embodied on the end of the bore 3 toward the combustionchamber. In FIG. 2, an enlarged view of the detail marked II of FIG. 1is shown, in the region of the valve seat 13. By means of a radialenlargement of the bore 3, a pressure chamber 5 is formed in the housing1 at the level of the pressure shoulder 9, and this chamber continues inthe form of an annular conduit, surrounding the outer valve needle 10,as far as the valve seat 13. A plurality of injection openings 7 areembodied in the valve seat 13, arranged in a first row 107 of injectionopenings and a second row 207 of injection openings, disposed axiallyoffset from it. Upon contact of the outer valve needle 10 with the valveseat 13, this valve needle closes all the injection openings 7 off fromthe pressure chamber 5, so that no fuel from the pressure chamber canreach the injection openings 7.

In the outer valve needle 10, there is an inner valve needle 12, whichis pistonlike and which on its end toward the combustion chamber has aconical pressure face 112 and a valve sealing face 14. If the innervalve needle 12 comes into contact with the valve seat 13, then thevalve sealing face 14 touches the valve seat 13 between the first row107 of injection openings and the second row 207 of injection openings.By the interplay of the outer valve needle 10 and the inner valve needle12, the rows 107, 207 of injection openings can be made to communicatewith the pressure chamber 5. If the outer valve needle 10 with its valvesealing face 11 is resting on the valve seat 13, then both rows 107, 207of injection openings are closed off from the pressure chamber 5. Ifonly the outer valve needle 10 lifts from the valve seat 13, while theinner valve needle 12 with its valve sealing face 14 rests on the valveseat 13, then only the first row 107 of injection openings is made tocommunicate with the pressure chamber 5, while the second row 207 ofinjection openings remains closed by the inner valve needle 12. Notuntil the inner valve needle 12 also lifts from the valve seat 13 is thesecond row 207 of injection openings made to communicate with thepressure chamber 5.

Via an inlet conduit 15 extending in the housing 1, the pressure chamber5 communicates with a high-pressure connection 17, which communicateswith a high-pressure fuel source, not shown in the drawing. When theinternal combustion engine is in operation, the high-pressure fuelsource here furnishes a predetermined high fuel pressure, so that in theinlet conduit 15 and thus also in the pressure chamber 5, this fuelpressure always prevails and forms a high-pressure fuel region.

Remote from the combustion chamber toward the bore 3, a piston bore 18embodied as a blind bore is made in the housing 1; it has a bottom face19. An outer piston rod 20 is disposed longitudinally displaceably inthe piston bore 18 and rests, with its face toward the combustionchamber, on the outer valve needle 10 and, with its face end 21 remotefrom the combustion chamber, it defines a control chamber 24 embodied onthe end of the piston bore 18. By means of a radial enlargement of thepiston bore 18, a spring chamber 8 is embodied in the housing 1, in theend region of the piston rod 20 toward the combustion chamber, and aspring 42 is disposed with pressure prestressing in this spring chamber.The spring 42 is braced in stationary fashion on the end remote from thecombustion chamber, and on its end toward the combustion chamber itrests on a spring plate 44, which is connected to the outer piston rod20, so that the spring 42 exerts a force in the direction of the valveseat 13 on the outer piston rod 20 and thus also on the outer valveneedle 10.

In the outer piston rod 20, there is an inner piston rod 22, which islongitudinally displaceable in the outer piston rod 20. On its endtoward the combustion chamber, the inner piston rod 22 rests on theinner valve needle 12, so that the inner piston rod 22 and the innervalve needle 12 move synchronously. FIG. 3 shows an enlargement of FIG.1 in the region of the control chamber 24. The control chamber 24 isdefined by the bottom face 19, the wall of the piston bore 18, and theface end 21 of the outer piston rod 20. The outer piston rod 20, on itsend remote from the combustion chamber, has an inward-projecting region27, so that the outer piston rod 20 and the face end 31, remote from thecombustion chamber, of the inner piston rod 22 define an inner controlchamber 29, which communicates with the control chamber 24 via aconnecting bore 28 in the outer piston rod 20. A stop face 23 isembodied in the interior of the outer piston rod 20 and limits thelongitudinal motion of the inner piston rod 22. In the closing positionof the fuel injection valve, that is, when both the inner valve needle12 and the outer valve needle 10 are resting on the valve seat 13, anaxial spacing remains between the stop face 23 and the face end 31,remote from the combustion chamber, of the inner piston rod 22.

The control chamber 24 communicates with the inlet conduit 15 via aninner throttle 25. Moreover, via an outer throttle 25, the controlchamber 24 communicates with a leak fuel chamber 30 embodied in thehousing 1. A longitudinally movable magnet armature 34 is disposed inthe leak fuel chamber 30 and has a sealing cone 32 on its end toward thecontrol chamber 24. The magnet armature 34 is acted upon by a closingspring 38, which presses the magnet armature 34 in the direction of thecontrol chamber 24. An electromagnet 36 is also disposed in the leakfuel chamber 30; when suitably supplied with current, it exerts anattracting force on the magnet armature 34 and moves it away from thecontrol chamber 24, counter to the force of the closing spring 38. If nocurrent is supplied to the electromagnet 36, then the magnet armature 34is pressed by the closing spring 38 in the direction of the controlchamber 24, and the sealing cone 32 closes the outer throttle 26. Whencurrent is supplied to the electromagnet 36, the magnet armature 34 ismoved away from the control chamber 24, and the sealing cone 32 uncoversthe outer throttle 26. In this position, fuel can flow out of thecontrol chamber 24 into the leak fuel chamber 30, via the outer throttle26. The magnet armature 34, sealing cone 32, and electromagnet 36 thusform a valve 33.

The mode of operation of the fuel injection valve is as follows: In theclosed state of the fuel injection valve, that is, when no fuel isinjected through the injection openings 7 into the combustion chamber ofthe engine, the sealing cone 32 closes the outer throttle 26. Throughthe inner throttle 25, the same fuel pressure prevails in the controlchamber 24 as in the inlet conduit 15. The result is a hydraulic forceon the face end 21 of the outer piston rod 20 and on the face end 31 ofthe inner piston rod 22, which transmit this force to the outer valveneedle 10 and the inner valve needle 12, respectively, so that the valveneedles 10, 12 are pressed into contact with the valve seat 13 and closethe injection openings 7. The ratio in terms of size between the faceend 21 and the pressure shoulder 9, or the pressure face 101 of theouter valve needle 10, is designed such that in this state of the fuelinjection valve, the hydraulic force on the face end 21 of the outerpiston rod 20 predominates. If an injection of fuel into the combustionchamber is to be accomplished, current is supplied to the electromagnet36, as a result of which the magnet armature 34 and thus also thesealing cone 32 move away from the outer throttle 26 and cause thecontrol chamber 24 to communicate with the leak fuel chamber 30 via theouter throttle 26. The flow resistances of the inner throttle 25 andouter throttle 26 are designed such that the fuel pressure in thecontrol chamber 24 drops as a result, in fact so far that the outervalve needle 10, because of the pressure face 101 and the pressureshoulder 9, experiences a greater hydraulic force than the hydraulicforce in the control chamber 24 that now also acts on the face end 21 ofthe outer piston rod 20.

As soon as the outer valve needle 10 lifts from the valve seat 13, ituncovers the first row 107 of injection openings, through which fuel isnow injected into the combustion chamber of the engine. As a result, thepressure face 112 of the inner valve needle 12 is now also acted upon byfuel pressure from the pressure chamber 5, so that the inner valveneedle 12 experiences an opening force. The remaining fuel pressure inthe control chamber 24 is so high, however, that the hydraulic force onthe face end 31 of the inner piston rod 22 still suffices to keep theinner valve needle 12 in the closing position, counter to the openingforce. In the course of the opening stroke motion, the outer piston rod20 finally comes into contact with the bottom face 19, and as a result,by means of an additional throttle restriction 45 that forms between theface end 21 of the outer piston rod 20 and the bottom face 19, thecontrol chamber 24 is largely closed off from the outer throttle 26.This position of the outer piston rod 20 is shown in FIG. 4. As aresult, the further inflow of fuel from the control chamber 24 to theouter throttle 26 is reduced, and the pressure in the inner controlchamber 29 drops still further. Because of the now lower hydraulicpressure in the inner control chamber 29, the inner valve needle 12,driven by the hydraulic force on the pressure face 112, and thus alsothe inner piston rod 22 move away from the valve seat 13, so that thesecond row 207 of injection openings is opened. The inner piston rod 22moves in the axial direction in this process, until it comes intocontact with the stop face 23 of the outer piston rod 20. By means ofthe successive opening of the two rows 107 and 207 of injectionopenings, a shaping of the injection course is achieved, in which at theonset of injection, fuel is injected into the combustion chamber of theengine with full pressure, but through only some of the injectionopenings 7, while in the main injection, it is injected through all theinjection openings 7 of both rows 107 and 207 of injection openings andthus also at a higher injection rate. To terminate the injection event,the current supply to the electromagnet 36 is stopped, and the sealingcone 32 on the magnet armature 34, driven by the closing spring 38,closes the outer throttle 26, so that because of the replenishing fuelflowing through the inner throttle 25, the fuel pressure of the inletconduit 15 builds up again in the control chamber 24 and presses boththe outer piston rod 20 and the inner piston rod 22 in the direction ofthe valve seat 13, so that the inner valve needle 12 and the outer valveneedle 10 are moved back into the closing position.

Provision can also be made for injecting fuel through only the first row107 of injection openings. For that purpose, the valve 33, which isformed by the electromagnet 34, the magnet armature 34, and the sealingcone 32, is closed again before the fuel pressure in the control chamber24 has dropped so far that the inner valve needle 12 opens. The outerthrottle 26 is then already closed again before the outer piston rod 20,with its end face 21, comes to rest on the bottom face 19 of the pistonbore 18. As a result, a hydraulic cushion is created between the endface 21 and the bottom face 19; it damps the opening motion of the outerpiston rod 20 and prevents a pressure drop in the control chamber 24,and so the inner piston rod 22 always exerts a sufficient closing forceon the inner valve needle 12.

Provision can also be made for the outer piston rod 20, in the openingstroke motion of the outer valve needle 10, to cover the inner throttle25 partially, so that the cross section of the inner throttle 25 isreduced, but the inner throttle is not closed completely. This can beachieved for instance by means of a residual annular gap between theouter piston rod 20 and the wall of the piston bore 18. Thecommunication of the control chamber 24 with the outer throttle 26 isassured for instance by means of radially extending grooves on the faceend 21 of the outer piston rod 20. As a result, the fuel inflow into thecontrol chamber 24 through the inner throttle 25 is reduced markedly, sothat the fuel in the control chamber 24 and, via the connecting bore 28,in the inner control chamber 29 as well drops further, and the innerpiston rod 22 and thus the inner valve needle 12 open in the mannerdescribed above.

1-12. (canceled)
 13. A fuel injection valve for internal combustionengines, comprising: a housing (1) in which a pistonlike outer valveneedle (10) is disposed longitudinally displaceably in a bore (3) andcooperates with a valve seat (13), embodied on the end of the bore (3)toward the combustion chamber, to control at least one injection opening(7), a control chamber (24) embodied in the housing (1), the pressure inthe control chamber (24) being regulatable by a valve (33), and by thepressure in the control chamber (24) a closing force is exerted at leastindirectly on the outer valve needle (10) in the direction of the valveseat (13), at least one pressure face (9; 101), embodied on the outervalve needle (10), which face is acted upon by the pressure in apressure chamber (5) embodied between the outer valve needle (10) andthe wall of the bore (3) and extending as far as the valve seat (13), sothat an opening force on the outer valve needle (10) results that isoriented counter to the closing force, and an inner valve needle (12)guided in the outer valve needle (10) and controlling at least oneadditional injection opening (7) on the valve seat (13), the inner valveneedle (12) being acted upon by the pressure in the control chamber (24)at least indirectly in the direction of the valve seat (13).
 14. Thefuel injection valve of claim 13, wherein, by the opening stroke motionof the outer valve needle (10), a throttle connection (45) is formed,whereby the inner valve needle (12) is no longer acted upon at leastindirectly by the pressure in the control chamber (24).
 15. The fuelinjection valve of claim 14, further comprising an outer piston rod (20)connected to the outer valve needle (10) and which moves synchronouslywith the outer valve needle (10) and has an end face (21), oriented awayfrom the outer valve needle (10), that is acted upon by the pressure inthe control chamber (24) and thus generates the closing force on theouter valve needle (10).
 16. The fuel injection valve of claim 15,wherein the throttle connection (45) is formed between the face end (21)of the outer piston rod (20) and a stationary bottom face (19).
 17. Thefuel injection valve of claim 15, further comprising an inner piston rod(22) connected to the inner valve needle (12) and which movessynchronously with the inner valve needle (12) and an end face (31)which is acted upon in the closing direction of the inner valve needle(12) by the pressure in the control chamber (24) and thus generates theclosing force on the inner valve needle (12).
 18. The fuel injectionvalve of claim 17, wherein the outer piston rod (20) is embodied as atube, and the inner piston rod (22) is guided in the outer piston rod(20).
 19. The fuel injection valve of claim 18, further comprising astroke stop face (23) embodied on the inside of the outer piston rod(20), and wherein the inner piston rod (22), in the opening motioneffected by the opening force on a pressure face (112) of the innervalve needle (12), comes to rest on the stop face (23).
 20. The fuelinjection valve of claim 18, wherein an inward-projecting region (27) isembodied on the end of the outer piston rod (20) remote from thecombustion chamber, whereby by means of the inside of the outer pistonrod (20), the inward-projecting region (27), and the face end (21) ofthe inner piston rod (22), an inner control chamber (29) is definedwhich communicates with the control chamber (24) only through aconnecting bore (28) in the outer piston rod (20).
 21. The fuelinjection valve of claim 13, wherein the inner valve needle (12) thepressure face (112) is not acted upon by the pressure in the pressurechamber (5) until after the outer valve needle (10) lifts from the valveseat (13), resulting in an opening force on the inner valve needle (12).22. The fuel injection valve of claim 13, wherein the control chamber(24) communicates via an inner throttle (25) with a high-pressure fuelregion and via an outer throttle (26) with a leak fuel chamber (30), inwhich a lower fuel pressure prevails then in the high-pressure fuelregion, and the outer throttle (26) can be closed by a valve (33). 23.The fuel injection valve of claim 22, wherein the outer piston rod (20),in the opening motion of the outer valve needle (10), partly closes theinner throttle (25) and thus establishes a reduced inlet cross sectionfrom the high-pressure fuel region into the control chamber (24). 24.The fuel injection valve of claim 23, further comprising a first row(107) of injection openings and a second row (207) of injectionopenings, axially offset from the first row are embodied at the valveseat (13), and the second row (207) of injection openings can be closedoff from the pressure chamber (5) by the inner valve needle (12), whilethe outer valve needle (10) is capable of closing off both the secondrow (207) of injection openings and the first row (107) of injectionopenings from the pressure chamber (5).